The invention relates to environmental control systems. More specifically, the invention relates to an environmental control system including an air cycle machine and an electrical machine.
An air conditioning system for an aircraft is designed to control airflow into the aircraft's passenger cabin as well as air temperature inside the passenger cabin. Most aircraft air conditioning systems operate on an air cycle refrigeration principle. Compressed air is obtained from an intermediate compressor stage of the aircraft's main engine, cooled with ambient air to near-ambient temperature in an air-to-air heat exchanger and then expanded in an air cycle machine to provide a stream of cooled, conditioned air. The conditioned air is supplied to the passenger cabin. Although somewhat expanded, the conditioned air is still compressed in order to pressurize the passenger cabin.
On occasion, the conditioned air might provide more cooling than necessary. The aircraft might climb to a high altitude, or the ambient air might be very cold. Whenever the conditioned air provides more cooling than necessary, the cooling is reduced by a complex combination of valves and controls.
Additionally, the engine supply pressure might sometimes be greater than required. Whenever this occurs, the pressure is reduced by throttling the compressed air. Throttling could be performed by modulating a bleed air pressure regulator valve, a pack flow control valve, or a bypass valve for the air cycle machine. However, throttling is a wasteful process that causes engine fuel consumption to be greater than necessary.